It has been common practice for many years for physicians to use a guidewire as an aid in the placement of a catheter at a selected location in the body of a patient. For example, among the most common uses of guidewires is in the placement of a catheter in a patient's blood vessel to perform a procedure at a specific location in the blood vessel. A number of protocols may be followed. For example, the guidewire first may be inserted into and advanced to the intended vascular site, with the catheter then being loaded onto and advanced along the guidewire to that vascular site. In another technique, the catheter and the guidewire may be assembled before insertion into the patient's vasculature so that they may be navigated together through the patient's blood vessels. In this technique, the distal tip of the guidewire may be permitted to extend slightly out of the distal end of the catheter. The physician can manipulate the guidewire from its proximal end so as to steer the distal end of the guidewire into selected branches of the patient s blood vessels until the intended site of treatment is reached. In another type of catheter, commonly referred to as a fixed wire catheter, the guidewire and catheter are formed as an integral, inseparable unit.
Common to all of the above catheter and guidewire systems is that the steering of the guidewire requires that the physician rotate the guidewire from its proximal end. It is intended in such procedures that the guidewire be sufficiently torsionally rigid to transmit controllably from the proximal to the distal end rotation applied at the proximal end. The rotation, coupled with the curve typically formed in the distal tip of the guidewire enables the guidewire to be selectively steered at blood vessel branches into a selected branch. Thus, by combined pushing and rotational manipulations, the leading, distal tip of the guidewire enables navigation of the guidewire to the site of intended vascular treatment.
Although the technology of small diameter steerable guidewires has developed significantly, the requirement that the distal tip be steered by rotating the guidewire from its proximal end sometimes presents difficulties that may preclude the guidewire from reaching the intended vascular site. In particular, the distal tip of the guidewire may not always follow as precisely as would be desired the rotation applied at the proximal end of the guidewire. This may result from any of a number of reasons. In order to effect rotation of the distal tip, it has been necessary to transmit that rotation controllably along the full length of the guidewire. In many cases, such as in coronary angioplasty procedures, the guidewire is relatively long, extending over approximately 175 cm. The guidewire typically has a diameter of from 0.012" to 0.018". A slight kink or permanent bend in the guidewire will cause it to lose its controllability, that is, the distal tip of a slightly kinked wire may tend to "whip" when the proximal end is rotated. Thus, in a kinked wire, rotation applied at the proximal end of the wire may not be followed with equal movement at the distal end of the wire. Instead, the wire may store the torque applied until it breaks free with the stored torque being released at the distal tip in a rapid rotational whipping of the tip as the stored portion is released.
Another difficulty presented with some types of fixed wire catheters, for example, of the type disclosed in U.S. Pat. No. 4,582,181 is that the guidewire is securely attached to the catheter in the region of the balloon. That tends to further limit the ability to steer the wire and presents an additional problem, that the balloon may become twisted in an hourglass configuration on the wire as the wire is rotated.
The foregoing difficulties with conventional steerable guidewires are accentuated when the guidewire and catheter are to be used in highly tortuous blood vessels, as is often encountered in coronary angioplasty. It would be desirable, therefore, to provide a catheter and guidewire combination which is not encumbered with the foregoing difficulties. It is among the objects of the invention to provide such a system.